The present invention relates to a communication control system used in a packet communication network and a method of controlling communication in the packet communication network in which a wired sub-network and a plurality of radio sub-networks are connected by learning type bridges.
Generally, in a packet communication network having a plurality of sub-networks, it is known to, when connecting sub-networks to each other, connect them using a bridge apparatus having a learning function (for example, JP-A-140034/1990).
In such a bridge system, a bridge apparatus has a learning table, a bridge for performing a relay of a packet registers a source address included in the packet and a received sub-network number in the learning table, and when a destination address included in the packet is registered in the learning table, the bridge transmits the packet to the registered sub-network. However, in case that the registered sub-network is a sub-network that has received the packet, the packet is discarded.
On the other hand, when the destination address is not registered in the learning table, the packet is simultaneously transmitted to all sub-networks connected to the bridge.
In case that the packet is not transmitted in a predetermined time interval from a terminal having a corresponding address, a set of the address and sub-network that are registered in the learning table is deleted due to out of time.
By means of the bridge system having such a learning function, simultaneous transmission of the packet to the sub-networks in which terminals do not exist (are not located) can be reduced and it become to be easy to structure a large scale network.
By the way, in the network in which a wired sub-network and a plurality of radio sub-networks are connected using the above-described bridge, in case that a terminal connected to, or located in one radio sub-network and conducting communication moves to other radio sub-networks, since an address of the terminal is registered together with the wired sub-network number in the bridge connecting the radio sub-network to which the terminal moves, to the wired sub-network, the packet transmitted to the terminal is not transmitted to a side of the radio sub-networks. And then, if the terminal that has moved (the said terminal) transmits the packet and the learning table is changed or if the set of the address and sub-network is deleted from the learning table due to out of time as mentioned above, the bridge becomes to start transmission of the packet transmitted to the terminal, to the side of the radio sub-network.
In the above-mentioned bridge system, when the terminal connected to one radio sub-network and conducting communication moves to other radio sub-networks, if the contents of the learning table of the bridge are not changed or deleted, the packet transmitted to the terminal is not transmitted to the side of the radio sub-networks, and as a result, there is a problem that reconnection during movement of the terminal needs time.